End-Botomian mass extinction
From Infogalactic: the planetary knowledge core

The Botomian age of the Early Cambrian epoch lasted from ca 524 to ca 517 million years ago. At the end of the Botomian age there was a mass extinction that wiped out a high percentage of the organisms for which fossils were found. Organisms which produced small shelly fossils were almost exterminated.[1]
Notes
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External links
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